1. Field of the Invention
This invention relates to an improved electrode supporting structure in an electron tube, and pertains more particularly to an improved means for centering and mounting the electrode within an envelope of a television camera tube.
2. Description of the Prior Art
In the prior art, certain photoconductive type pickup tubes, commonly known as camera tubes, are often used in television broadcast cameras. Conventional tubes of this type generally comprise a tubular glass envelope within which is contained several electrode elements, including an elongated hollow tubular beam focusing electrode, typically known as the "G3" electrode.
The operating characteristics of the camera tube may be adversely affected if its electrodes become even slightly misaligned. For example, in the usual color broadcast camera, there are three camera tubes aligned by their outer envelopes in a yoke within which a magnetic field is applied. Each of these three camera tubes transmits an image, for example, in red, blue or green, to a display screen in substantial register to obtain a color picture. If the focusing electrode of each tube is not properly centered within the magnetic field, the response of each tube will not be homogeneous and the register will be poor. Accordingly, for good register it is desirable that the optics of each camera tube be substantially the same which requires, in part, that the focusing electrodes be concentrically supported with respect to the tube envelope.
There are many known arrangements for supporting and positioning electrodes within the tubular envelope of a camera tube. A typical supporting structure includes a plurality of spaced spring clips such as those shown in U.S. Pat. No. 3,038,094, issued June 5, 1962 or finger-like members as shown in U.S. Pat. No. 2,951,962, issued on Sept. 6, 1960. These may be disposed on one end or both ends of an elongated cylindrical electrode. The spring elements are of flexible material and are pressed against the inner surface of the wall of the tubular envelope to support and position the electrode. Other known electrode supports include a conical shaped bulb-spacer as described in U.S. Pat. No. 2,897,389, issued on July 28, 1959 and a ring with a flared portion as shown in U.S. Pat. No. 3,183,388, issued on May 11, 1965. The conical spacer and flange portion in these two arrangements, respectively, are formed of resilient material and yieldably engage the inner walls of the tube envelope when they are slid into the bulb envelope.
The problem with these arrangements, and other known electrode supports, is that the structural members that are supporting the electrodes are also relied upon to provide the desirable and critical concentricity of the electrodes within the tube envelope. Many factors, such as vibration, shock and thermal stresses, may cause these resilient and flexible supports to shift position relative to the envelope or the electrode. For example, even an electrode that is fixtured during fabrication to be substantially concentric with the envelope may lose its concentricity upon subsequent thermal processing. Such supporting structures, structurally susceptible to concentricity deviations under normally expected operating conditions, are not desirable.